In planar IGBTs having planar MOS structures, a planar gate is used. Accordingly, a region necessary for device operation must be ensured, and miniaturization is limited. Moreover, a high ON voltage imposes a limitation. Meanwhile, trench IGBTs have trench (vertical) gate structures, and can therefore be miniaturized (e.g., see Patent Document 1). Further, ON voltage characteristics can be improved by utilizing the electron injection effect at trench bottoms.